1. Field of the Invention
The present invention relates to a polymer modified pigment having a polymer on a pigment surface, and a production process of the same.
2. Description of the Related Art
Since pigments are typically insoluble colorants, the uniform dispersion of pigment particles in media such as solvents or resins is an important factor in the production of paint, printing ink or color filters and the like and in the coloring of plastics.
Since the dispersibility of a pigment is largely dependent on the surface properties of the pigment particles, efforts to improve dispersibility have been made using various surface treatments. Examples of these treatment methods include rosin treatment, treatment with various types of surfactants such as cationic surfactants, anionic surfactants or nonionic surfactants, pigment derivative treatment and polymer treatment.
Among these treatment methods, examples of polymer treatment methods, which are used to improve dispersibility by coating a polymer onto a pigment surface, include in-situ polymerization, phase separation (coacervation) and drying-in-liquid.
Among these, in-situ polymerization is a method that has been employed in the past, and is described in Patent Documents 1 to 7. All of these methods are carried out under aqueous conditions. For example, in the methods described in Japanese Unexamined Patent Application, First Publication No. 2004-189928 (Patent Document 1) and Japanese Unexamined Patent Application, First Publication No. 2004-189929 (Patent Document 2), a polymer modified pigment is obtained by stably dispersing a pigment in an aqueous medium using a surfactant or water-soluble polymer followed by polymerizing a monomer. In addition, in the methods described in Japanese Unexamined Patent Application, First Publication No. 2005-097517 (Patent Document 3) and Japanese Unexamined Patent Application, First Publication No. H10-316909 (Patent Document 4), a polymer modified pigment is obtained using a polymerizable surfactant. In addition, in the method described in Japanese Unexamined Patent Application, First Publication No. 2004-155818 (Patent Document 5), a polymer modified pigment is obtained by using an alkylene oxide chain-containing compound having a polymerizable functional group and polymerizing a monomer in a system in which a pigment is dispersed.
However, all of these methods had problems consisting the pigments able to be used being specified since the pigment is required to be in a state in which it can be stably dispersed in an aqueous medium, dispersion stability of the resulting polymer modified pigment being only able to be obtained in an aqueous medium, and dispersion stability being unable to be obtained in an organic solvent.
Although the method described in Japanese Unexamined Patent Application, First Publication No. H13-72887 (Patent Document 6) is a method for obtaining a polymer modified pigment by mixing a pigment and a monomer followed by suspension polymerization using a dispersion stabilizer, this method prevents the obtaining of fine polymer modified pigments.
In addition, the method described in Japanese Unexamined Patent Application, First Publication No. 2005-120365 is a method for obtaining a polymer modified pigment by polymerizing a monomer in the presence of a pigment of which the surface thereof has been precoated with a silane coupling agent in a mixed solvent consisting of a hydrophilic organic solvent and water. However, this method cannot be applied to organic pigments that are poorly miscible with silane coupling agents, that is, have poor affinity with silane coupling agents.
Examples of in-situ polymerization methods not using water for the solvent are described in Japanese Unexamined Patent Application, First Publication No. 2004-2501, Japanese Unexamined Patent Application, First Publication No. 2004-18736, Japanese Unexamined Patent Application, First Publication No. 2004-35592, Japanese Unexamined Patent Application, First Publication No. 2004-083660, Japanese Unexamined Patent Application, First Publication No. 2004-107523 and Japanese Unexamined Patent Application, First Publication No. 2004-107524 (Patent Documents 8 to 13). All of these methods consist of carrying out in-situ polymerization in a non-aqueous solvent having a dielectric constant of 1.5 to 20 and surface tension of 15 to 60 mN/m. However, since all of the methods described in these references require the use of a surface-modified pigment and that the pigment be stably dispersed with a specific dispersion stabilizer, they are not universal methods.
In this manner, although there are various techniques used to carry out in-situ polymerization, techniques have not obtained yet that can be applied to general-purpose pigments and allows the obtaining of a polymer modified pigment demonstrating satisfactory dispersion stability even in an organic solvent.
An object of the present invention is to provide a polymer modified pigment demonstrating satisfactory dispersion stability even in an organic solvent, and a process for producing a polymer modified pigment demonstrating satisfactory dispersion stability even in an organic solvent that can be applied to general-purpose pigments.
As a result of conducting extensive studies to solve the aforementioned problems, the inventors of the present invention found that a polymer modified pigment, having a polymer obtained by copolymerizing a specific polymer soluble in a non-aqueous solvent with at least one kind of polymerizable unsaturated monomer, demonstrates satisfactory pigment dispersibility, thereby leading to completion of the present invention.